Contemporary robotic work tools are becoming more and more advanced and are able to perform more and more advanced tasks such as executing advanced operation patterns. In the example of lawnmower robots the advanced working pattern may be a complicated mowing pattern based on the layout of a garden including bushes, garden islands and other structures. To successfully navigate such complicated areas some contemporary robotic work tools employ various navigation techniques three of the main being deduced reckoning (also known as dead reckoning), satellite navigation or using boundary wires.
One factor that complicates the working pattern is the presence of different obstacles or structures inside a working area. For the example of the robotic work tool being a lawnmower robot and the work area being a garden, the obstacles may be bushes and trees and the structures may be a porch or a shed.
Such structures are usually fixed or permanent and will not change over time and can thus be marked with a boundary marker such as a boundary wire that transmits an electric current that is detected by the robotic work tool. Alternatively they can be marked in a map of the work area and the robotic work tool includes the coordinates of such structures in its operating pattern so that the structures are avoided. Such technologies are well known in the art.
However, obstacles may change over time and may also not always be present. For example, a user may dig a hole in his garden for example to service some pipes and this hole would not be a permanent feature of the garden. Furthermore, the user may want that one area should not be serviced at a specific time such as when a child is playing in one corner of the garden. Such areas will hereafter be referred to as temporary or virtual obstacles.
To mark such obstacles with prior art technologies is cumbersome as it requires that boundary wires are dug down or that the map is reprogrammed. Something which can be cumbersome to a user, especially if the obstacle will only be present for a short time.
The international patent application WO99/59042A discloses a robotic system for systematically moving about an area to be covered. The system includes at least one boundary marker located along the outer edge of the area to be covered, a robot with a navigation system and a sensor unit. The navigation system navigates the robot in generally straight, parallel lines from an initial location and turns the robot when the robot encounters one of the boundary markers, thereby to systematically move about the area to be covered. The sensor unit senses proximity to one of the at least one boundary marker. The system may further comprise obstacle markers that are also sensed by the robot.
The disclosure teaches on page 7; lines 17 to 20 that obstacles that are above ground may be detected by mere collision detection, whereby the obstacle itself is the obstacle marker and the sensing is the collision detection. This will increase the wear and tear of a robotic work tool as it will be subjected to numerous collisions. Furthermore, such detection is highly unsuitable for virtual obstacles.
The disclosure also teaches on page 9 that the obstacle markers are wires and a manner of differentiating between obstacle markers and boundary markers is given. As has been discussed above, such wires need to be dug down in the ground and as such require much work to be done which may be especially cumbersome if it is only for a temporary marker.
The disclosure further teaches on page 10 that the obstacle markers may be a post having a bar code written on it which is detected through a bar code reader. Such barcodes must therefore be visually detected which limits the placement, the distance/size of the (virtual) obstacle and the arrangement is also sensitive to debris blocking the barcode reader's lens.
Even though the problems above have been discussed for lawnmower robotic work tools, the same or similar problems exist also for other robotic work tools.
There is thus a need for a manner of enabling indicating obstacles, that is easy to install, is not sensitive to debris or waste, and does not increase the wear and tear of a robotic work tool.